RFI (radio frequency interference) and EMI (electromagnetic interference) is a problem that is commonly encountered in the design and operation of electronic equipment. EMI/RFI as it is commonly known, can cause electronic equipment to not function properly or not function at all. Today with the advent of fast, more powerful and high frequency operating electronic devices, the prevention of EMI/RFI is of paramount importance.
Typically, electronic equipment is designed to fit within a metallic cabinet which help to reduce the occurence of EMI/RFI. These cabinets or shells generally have openings, such as doors or panels which are removable so that the electronic equipment may be serviced or replaced. The discontinuity between the cabinet frame and the door or panel allows the EMI/RFI to pass into or out of the cabinet, thereby causing the failure of the electronic equipment in or around the cabinet.
One of the most commonly used EMI/RFI shielding materials is a metal strip known as fingerstock. Fingerstock generally is formed of beryllium copper or phosphor bronze and is bent into a V or U shape with a number of resilient elements or "fingers" extending out from the center of the material on at least one of the arms. Examples of such fingerstock are shown in U.S. Pat. No. 3,277,230; 3,504,095 and 4,572,921. Fingerstock is difficult to install and requires that a substantial closure or compression force be applied to it in order to achieve electrical continuity between the door or panel and the cabinet. Additionally, the fingerstock, being metal, is susceptible to fatigue causing the fingers to break off or to retain a permanent compression set. In either event, the shielding properties of the fingerstock is substantially degraded or destroyed. Metal fingerstock therefore requires routine and regular maintenance which adds to its cost.
Other alternatives to fingerstock include wire mesh covered elastomers, conductively filled elastomers and a spirally formed "O" ring type of gasket. Each of these materials provide adequate EMI/RFI shielding, however they require a high level of compression to ensure adequate electrical continuity between the substrates being joined. Additionally, these alternatives are more expensive to manufacture than fingerstock, making their use, especially in the consumer electronics market less acceptable.
The present invention provides an alternative to metal fingerstock which overcomes the shortfalls of fingerstock or the other alternatives mentioned above and which is inexpensive, simple to manufacture and apply.